Cryogenic gas-assisted mechanical refrigeration cooling system apparatus and method

ABSTRACT

A method and apparatus for cooling articles, particularly having applications for chilling extrusions, food, and similar articles, utilizing a vaporized cryogen in combination with conventional refrigeration. The vaporized cryogen provides a substantially dry atmosphere from which an evaporator of the conventional refrigeration unit may remove energy. The vaporized cryogen may be circulated at a controlled velocity to provide improved temperature control in the system.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/173,057 filed Jun. 17, 2002, which claims thebenefit of U.S. Provisional Application Ser. No. 60/298,856 filed Jun.15, 2001, U.S. Provisional Application Ser. No. 60/298,851 filed Jun.15, 2001, U.S. Provisional Application Ser. No. 60/299,131 filed Jun.15, 2001, U.S. Provisional Application Ser. No. 60/298,854 filed Jun.15, 2001, and U.S. Provisional Application Ser. No. 60/298,852 filedJun. 15, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a method and apparatusfor cooling extrusion articles, and more specifically to substantiallyvaporizing a liquid cryogen and then circulating the vaporized cryogenthrough a cooling chamber, circulating the vaporized cryogen incombination with refrigeration assistance, circulating the vaporizedcryogen through a cooling chamber including sizing and/or calibrationtools, circulating the vaporized cryogen through a hollow in the articleitself or a combination of the aforementioned to cool an extrudate. Theinvention is particularly useful as an extrusion chiller, and may alsobe utilized for chilling foods. Additionally, many other applications ofthe invention will become apparent to those skilled in the art upon areview of the following specification and drawings.

BACKGROUND OF THE INVENTION

[0003] Certain continuously extruded materials, e.g., rubber products,plastic products, metal products, wood composites, must be cooled afterpassing through the extrusion operation in order to prevent deformation.In conventional extrusion operations, the extruded materials, be ithose, pipe, rod, bar or any other shape may deform from its own weightif the temperature was not decreased rapidly after leaving the extruder.Cooling the product rapidly creates at least a minimum amount ofrigidity in the extrudate such that the manufacturer can cut, stack orotherwise handle the extrudate without unwanted deformation. If theproduct is not cooled effectively and quickly, the resultant deformationcan lead to excessive rates of rejection of the manufactured or extrudedproduct. Further, the rate at which the extrudate is cooled directlyaffects the rate at which product may be produced. In other words, thefaster an extrudate is cooled, the faster the end product can beproduced.

[0004] Historically, water-based cooling systems have been utilized withwater as the primary medium for cooling articles, including extrusions.For example, conventional extrusion chilling systems employ a “cooling”chamber downstream from the extruder. The extrusion is fed through thecooling chamber, wherein the extrusion can be sprayed with water, orpartially/fully submerged in water in order to chill the extrusion.Various other components may also be included in such systems, such as avacuum sizing chamber intermediate the extruder and the cooling chamber.The vacuum sizing chamber can be used for both solid and hollowextrusions and employs an external vacuum pump to create a vacuum toassist the extrusion in maintaining its shape while it cools. Water canalso be used in the vacuum chamber to cool the extrusion while thevacuum supports the shape. However, cooling water systems have severaldrawbacks. Many products are adversely affected if contacted with water.Thus, extra care must be taken to avoid such occurrences. Extrusionspeeds are limited because the cooling water generally has a welldefined heat transfer capability and thus can only cool the freshextrudate in accordance therewith. In practice, an optimum coolingtemperature of approximately 50° F. is achievable from a cost-effectivestandpoint, which limits the manufacturer's ability to cool extrusionsquickly. Additionally, cooling water systems require excessive floorspace and also require treatments or special additive packages toprepare and maintain proper water chemistry, as well as to preventscaling and bacterial growth, which add significantly to the costthereof.

[0005] Coolant mediums other than water which have been used in coolingprocesses can be referred to collectively as refrigerants, includingcryogens. Cryogens include liquid nitrogen, liquid carbon dioxide,liquid air and other refrigerants having normal boiling pointssubstantially below minus 50° F. (−46° C.). Prior art methods of coolingarticles using cryogens disclose the benefits of fully vaporizing acryogen into a gaseous refrigerant prior to contact with the articles tobe cooled. Cryogens due to their extremely low boiling point, naturallyand virtually instantaneously expand into gaseous form when dispersedinto the air. This results in a radical consumption of heat. The ambienttemperature can be reduced to hundreds of degrees below zero(Fahrenheit) in a relatively short time, and much quicker than may berealized with a conventional cooling water system. The extremedifference in vaporized cryogen and the extruded product allows themanufacturer to quickly cool an extrudate.

[0006] However, these prior methods of cryogenic cooling failed torealize the advantages, both in increased efficiency and in improvedsystem control, that can be achieved by utilizing forced gas convectionin combination with vaporized nitrogen or any other refrigerant. Somedisadvantages of previous cryogenic cooling systems include lowerefficiency and limited options for controlling the cooling process. Suchsystems generally rely exclusively on the cooling effect of therefrigerant, to lower the ambient temperature and chill the article.Although previous methods utilize forced convection to ensure completevaporization of the cryogen, no methods use forced gas convection tocontrol the rate of cooling of the article by controlling the wind chilltemperature. Consequently, the only control variable in the previousmethods to adjust (lower) the temperature is the introduction of aliquid cryogen into the system. In contrast, utilization of forced gasconvection adds a wide range of variable control to adjust the effectivetemperature, up or down, by controlling the velocity at which therefrigerant is circulated over/around the article to be cooled. Such aforced gas convection system is disclosed by Thomas in U.S. Pat. No.6,389,828, incorporated herein in its entirety by reference thereto.

[0007] The basis of forced gas convection is the principle thatincreasing velocity of a refrigerant over a heated surface, such as byblowing, greatly enhances the transfer of heat from that surface. In thecontext of cold temperatures, this principle is probably better knownindirectly from the commonly used phrase “wind chill” temperature, whichis frequently reported on TV or radio by weather announcers. In thatcontext, wind chill temperature is what the temperature outside “feels”like, taking into account the ambient temperature and the prevailingvelocity of the wind. The stronger (higher velocity) the wind, the lowerthe temperature “feels,” compared to if there were no wind present.Forced gas convection cooling systems, as disclosed herein, takeadvantage of this “wind chill” affect in their ability to remove heatfrom an object faster with a constant temperature of a gas. In otherwords, if a 400° F. object is placed in a constant 75° F. atmospherewithout velocity of the surrounding atmosphere, the transfer of energyfrom the object to the surrounding atmosphere by convection is muchslower than if the atmosphere has a velocity over/around the object. Anincrease in velocity will increase the rate of energy transfer, eventhough the temperature of the atmosphere is constant. The rate ofcooling can be increased or decreased by manipulating the velocity ofthe cooling medium as the temperature of the medium remains constant.This principle is advantageously utilized to significantly enhance thecooling efficiency of the system by creating, and controlling, “windchill” temperature during the cooling process. As a result, theefficiency of the process is increased while simultaneously reducing thesize, which is typically the length, of the cooling system.

[0008] However, the previous method disclosed by Thomas utilizes only ameasurement of the ambient temperature within the cooling chamber toadjust the velocity and discharge of cryogen. An extrudate leaving acooling chamber does not necessarily need to be cooled to an eventemperature throughout, but may rely on “equilibrium cooling.” Thisprinciple is advantageously utilized according to the invention tosignificantly enhance the cooling efficiency of the system by creatingand controlling the “wind chill” temperature during the cooling processin relation to a measurement of the temperature of the product afterleaving the cooling chamber. The basis for “equilibrium cooling” is thata mass having two different temperature zones, or a temperaturegradient, will exchange energy between the two zones until an“equilibrium” temperature is reached. Thus, a manufacturer can reducecooling time and cooling system length by super-cooling at least 51% ofthe extrudate mass to form a “skin” having sufficient rigidity such thatthe extrudate may be handled as needed and then allowing the“equilibrium cooling” effect to take place after the extrudate has leftthe cooling system.

[0009] Another type of prior art cooling system utilizes a device calleda “calibrator,” and typically multiple such calibrators, to coolextrusions. A calibrator is a tool which generally has a central openingthrough which the extrusion is fed, the central opening having a surfacewhich is generally in contact with the surface of the extrusion as it isfed through. As a result of contact with the surface of the extrusion,the calibrator acts as a heat sink and the heat is conducted to thecalibrator and away from the extrusion thus cooling the extrusion. Sincecooling of the extrudate tends to make the material contract or changeshape, a vacuum generated by external vacuum pumps is generally drawnthrough grooves in the calibrator inner surface making contact with theextrudate. This vacuum assists in maintaining the shape of theextrudate. To enhance the heat transfer from the extrusion, internalpassages or circuits are provided in the calibrator through which acoolant is circulated. Typically, the coolant is water, but liquidnitrogen is also known to have been used to some degree. However,circulating liquid nitrogen through the cooling circuits has met withsome difficulties regarding contact of the liquid nitrogen with thecalibrators. Additionally, cooling water systems include the inherentproblems associated therewith as discussed above. The aforementionedU.S. Pat. No. 6,389,828 to Thomas discloses that it is preferable tofirst vaporize a liquid cryogen, such as liquid nitrogen, and then tocirculate the super-cold vapor/refrigerant through the cooling circuitsinstead of the liquid cryogen, which thus requires a system forvaporizing the liquid cryogen prior to circulation through the coolingcircuits of the calibrator. Although such a method is an improvementover the prior art, the system may still require the use of externalvacuum pumps as previously stated. The present invention provides for acalibration tooling chamber utilizing forced-gas convection of acryogenic refrigerant in combination with a calibrator tooling or sizingtemplate having a plurality of fins in an outer surface thereof to allowthe extrudate to be cooled at an effective rate. This eliminates theneed for internal passages, and thus the additional manufacturing costsassociated with the required set-up/connection/break-down of theequipment between different product runs. Further, the presentinvention, by use of a forced gas convection cooling chamber, provides ameans of generating an internally induced vacuum to assist the extrudatewithout the requirement of a separate external pump. External vacuumpumps are expensive, require continued maintenance and repair, are noisyand they must be replaced often.

[0010] Many extruded articles include at least one hollow, such as pipe,hose, etc., or may contain several hollow portions. Prior art coolingsystems provide the manufacturer with only the ability to cool anextrudate from an outer surface thereof by contact with a cooler medium(liquid, gas or solid depending on the system). Depending on the productgeometry, however, a significant amount of an extrudate's mass may bepositioned inward of the outer surface and between several hollowportions. Thus, it is difficult to quickly and effectively cool such anextrudate quickly because the cooling medium does not make contact withthose portions. The present invention provides an apparatus and methodfor cooling an extrudate having at least one hollow by circulating avaporized cryogen through the hollow, preferably in combination withexterior cooling techniques as disclosed in U.S. Pat. No. 6,389,828 andtaught herein. This provides for increased cooling capacity and control,as well as reduced cooling system length requirements.

[0011] Conventional refrigeration systems have found limited success inthe extrusion cooling industry and other industrial coolingapplications. Mechanical refrigeration systems generally consist of acompressor, a condenser, a storage tank, a throttling valve, and anevaporator connected by suitable conduits. The refrigerant is a liquidwhich partly vaporizes and cools as it passes through the throttlingvalve. Common refrigerants include ammonia, sulfur dioxide, and varioushalides of methane and ethane. CFCs have been used extensively in thepast, but due to their adverse environmental effects, are generallyavoided now. In operation, the compressor inputs work to maintain nearlyconstant pressures on either side of the throttling valve. The mixedliquid and vapor entering the evaporator from the throttling valve iscolder than the air surrounding the evaporator, thus the liquid/vaporrefrigerant absorbs heat from the interior of the refrigerator box orcold room and completely vaporizes. The vapor is then forced into thecompressor, where its temperature and pressure increase as the result ofcompression. The compressed vapor then travels into the condenser, whereit cools down and liquefies as the heat is transferred to the colderatmosphere surround the condenser's cooling coils. The liquefiedrefrigerant is then stored in the storage tank for re-release throughthe throttling valve into the evaporator.

[0012] Conventional mechanical refrigeration systems, although costefficient to operate in limited situations where cooling is not requiredto extremely low temperatures, are limited in their cooling capacity forextrusion cooling systems and other rapid cooling application withinindustry, and cannot reach extremely cold temperatures. This is dueprimarily to the evaporator coils becoming clogged with ice as themoisture in the moist air contained in the refrigerator box freezes whenthe moist air passes the coils. Once the coils are covered in a skin ofice or frost, or clogged altogether, the heat transfer rate is greatlydiminished and the coil must be defrosted. This requires costly downtimethat negates the feasability of using mechanical refrigeration forcooling to extremely low temperatures. Similar problems facevapor-absorption refrigeration systems.

[0013] Accordingly, there is a need for a method and apparatus forcooling articles which can provide one or more properties such asimproved efficiency, reduced size of the cooling system, and/or acooling system that does not require external vacuum pumps.

SUMMARY OF THE INVENTION

[0014] A method and apparatus for cooling articles are provided whichcan utilize the dispersion of a liquid cryogen into a feed chamberwherein the liquid cryogen is substantially vaporized and thencirculated through a cooling chamber containing the article to becooled. The vaporized cryogen can be further circulated though thecooling chamber at a controllable velocity, over/around the surface ofthe article to be cooled and/or tooling, in order to regulate the rateof cooling the article by controlling the wind chill temperature, basedupon the principles of forced gas convection.

[0015] A presently preferred cryogen is liquid nitrogen. The liquidnitrogen can be dispersed into a feed chamber in a controlled mannerusing a valve, which can be operated by a controller, such as amicroprocessor. Since the temperature in the feed chamber is much higherthan the boiling point of the liquid nitrogen, a high BTU (BritishThermal Unit) and expansion rate is captured thereby producing anextremely effective refrigerant. The feed chamber can be communicatedwith a cooling chamber into which the vaporized cryogen can becirculated by a fan, or other device for circulating a gas and/orvaporized cryogen. Either the feed chamber or the cooling chamber can bevented to dissipate pressure generated as the liquid nitrogen rapidlyexpands to gaseous form. The fan can preferably be a variable speed fan,or other variable speed circulation device, for circulating thevaporized cryogen through the system at a controllable velocity to takeadvantage of principles of forced gas convection. The fan can be locatedin the feed chamber to aid in substantially vaporizing the liquidcryogen. However, considering the relatively high temperature utilizedin the cooling chamber compared to the boiling point of the cryogen,even without the fan, the liquid cryogen will virtually completely andinstantaneously vaporize as it is injected into the feed chamber. Thefan can be operated by the controller which can regulate the speed ofthe fan to provide improved temperature control over the system bycontrolling the wind chill temperature in the cooling chamber. Thesystem can also include a temperature sensor, connected to thecontroller, for monitoring the temperature in the cooling chamber, andto calculate the wind chill temperature. An additional externaltemperature sensor may be provided and connected to the controller. Theexternal temperature sensor is adapted to monitor the temperature of anarticle after the article has exited the cooling chamber and relays theoutput signal to the controller, which can operate the fan and valve toprovide improved temperature control over the system by controlling thewind chill temperature in the cooling chamber in relation to thearticle's exit temperature. A heating device can be provided to increasethe temperature in the cooling chamber, if needed. The speed of the fancan be controlled by the microprocessor to circulate the refrigerant ata high volume (CFM) to maximize the cooling efficiency, therebyminimizing cryogen consumption. Essentially, the rate of cooling of thearticle can be increased for a given amount of cryogen dispersed intothe feed chamber by increasing the speed of the fan. Another way toexpress this concept is to say that the “effective temperature” in thechamber can be reduced by increasing the speed of the fan. The articlesto be cooled can be delivered into the cooling chamber by means of aconveyor belt, or various other ways of feeding articles, for examplepulling extrusions, through the cooling chambers.

[0016] The cooling system can also employ a plurality of coolingchambers, preferably adjacent, each of which can be individuallycontrolled by one or more controllers. The controllers can manage thespeed of the fan and the nitrogen injection for each individual coolingchamber, thereby providing for maximum heat exchange rates forefficiency and effectiveness. Each cooling chamber can be equipped withits own temperature sensor, nitrogen injection valve to control theintroduction of nitrogen into the cooling chamber, and variable speedfan for circulating refrigerant through the cooling chamber.

[0017] In general operation, the temperature sensor detects thetemperature in the cooling chamber, or of the circulated refrigerant,and the external temperature sensor detects the temperature of anarticle that has exited the cooling chamber and each feed the respectiveinformation to the controller. The controller can be programmed with adesired temperature to which the temperature inside the cooling chamberis to be regulated or to the desired temperature of the article as itexits the cooling chamber. The controller can also control the nitrogeninjection valve and the speed of the fan to cause the temperature in thecooling chamber to correspond to the desired temperature or temperaturecalculated to cool the article to the desired article temperature. Anequation for calculating the “effective temperature,” i.e. wind chilltemperature, from the speed of the fan and the ambient temperature inthe cooling chamber can be programmed into the microprocessor. The speedof the fan can thus be regulated to increase or decrease the rate ofcooling of the article, by adjusting the effective temperature in thecooling chamber, in order to maximize the efficiency of the coolingsystem. Principles of forced air convection can thus be utilized toincrease cooling efficiency while minimizing the consumption ofnitrogen.

[0018] Likewise, principles of forced gas convection can be utilized incombination with principles of “equilibrium” cooling to quickly coolsurfaces of an article to produce a “skin” of sufficient rigidity forfurther handling. A “skin” may be super-cooled (cooled to a temperaturebelow the desired article temperature), but the core remaining at atemperature higher than the desired article temperature. The warmer coreregions continue to transfer energy to the cooler “skin” regions afterexiting the cooling chamber until the two regions reach an “equilibrium”temperature. Thus, the cooling systems of the present invention canproduce the required cooling with less line space. The fan additionallypermits improved system control over the effective temperature in thecooling chamber. A method of cooling an article using “equilibrium”cooling according to the invention comprises the following steps: a)introducing liquid cryogen into a feed chamber wherein said liquidcryogen is substantially vaporized; b) circulating said vaporizedcryogen from said feed chamber into a separate cooling chambercontaining said article to be cooled; c) circulating said vaporizedcryogen at a controllable velocity from said feed chamber into saidcooling chamber and around said article to create a wind chilltemperature in said cooling chamber to increase a rate of cooling ofsaid article; d) sensing the temperature in at least one of said feedchamber and said cooling chamber; e) calculating said wind chilltemperature in said cooling chamber, said wind chill temperature being afunction of the temperature in said cooling chamber and the velocity atwhich said vaporized cryogen is circulated through said cooling chamberover said article; f) selecting a desired product temperature; g)sensing the temperature of the article prior to entering said coolingchamber and calculating a difference between said desired producttemperature and said temperature of the article prior to entering saidcooling chamber; h) calculating an amount of energy that must be removedfrom said article during the resonance time said article is in saidcooling chamber necessary to cool greater than 50% of the mass of saidarticle to a super-cool temperature below the desired producttemperature, such that the difference between said super-cooltemperature and said desired product temperature is greater than orequal to said difference between the sensed temperature of the articleprior to entering the cooling chamber and the desired producttemperature, said amount of energy being a function of the heatcapacity, thermal conductivity, and resonance time of said article insaid cooling chamber; i) calculating a wind chill temperature necessaryto remove said amount of energy; and i) controlling said velocity tocause said wind chill temperature to correspond to said wind chilltemperature necessary to remove said amount of energy.

[0019] Another embodiment of the invention is a cooling system which,utilizing wind chill temperatures, is particularly adapted to vaporize aliquid cryogen and circulate the refrigerant over/pass metal tools foran article within the tool. Specific examples of such tools are acalibrator and a sizing template, which are commonly used to coolextruded articles. The metal tools are provided with a plurality of finsextending from an outer surface thereof that provide for increasedexternal surface area. The metal tools are enclosed within a coolingchamber, or chambers and the metal tools, such as calibrators, throughwhich an extrusion is passed to be cooled, is itself, along with theextrusion, cooled within a cooling chamber. Advantageously, such asystem can be vacuum assisted without the need for costly externalvacuum pumps. The cooling chamber includes an outlet throat throughwhich refrigerant enters the cooling chamber and an inlet throat throughwhich the refrigerant exits the cooling chamber and is recirculated by afan. By providing the outlet throat with a cross-sectional area lessthan the cross-sectional area of the inlet throat, the fan is thus“starved” and a vacuum is induced within the cooling chamber.Preferably, a restrictor plate or other suitable mechanism is providedthat can be operated to vary the cross-sectional area of the outletthroat, inlet throat, or both.

[0020] Another embodiment of the invention is a cooling system which,utilizing principles of forced gas convection, is particularly adaptedto vaporize a liquid cryogen and circulate the vaporized through ahollow within an extrudate. The cooling system includes similarcomponents as previously discussed, except the vaporized cryogen iscommunicated to the hollow through an inlet bore provided in an extruderdie and mandrel. Preferably, the cooling system is “captive” and thevaporized cryogen is recirculated. For example, the vaporized cryogencan exit the hollow within a closed cutting chamber. The cutting chambercommunicates with a fan via a return conduit. Operation of the system isthe same as previously described. Optionally, the cooling system is usedin combination with a cooling system to simultaneously cool the outersurface of the extrudate, such as a metal tool cooling system accordingto the invention.

[0021] In another embodiment, a cooling system is provided whichutilizes the principles of forced gas convection of a vaporized liquidcryogen and is assisted by at least one conventional refrigeration unit.The cooling system may include similar components, such as previouslydiscussed with respect to the forced-gas convection systems tointroduce, vaporize, circulate at a controllable velocity, and furtherincludes an evaporator of a refrigeration unit positioned inenergy-absorbing communication with the circulating vapor. A pluralityof cooling chambers may be used with a plurality of refrigeration units.Preferably, any moisture containing air is purged from the coolingsystem with vaporized cryogen prior to operation of the refrigerationunit. The refrigeration unit can be operated by the controller toprovide a desired amount of cooling, or heat removal, to the circulatedvapor. Operation of the refrigeration unit provides cooling assistanceand thereby reduces the consumption of liquid cryogen to lower theambient temperature of the vapor within the system.

[0022] Other details, objects, and advantages of the invention willbecome apparent from the following detailed description and theaccompanying drawing figures of certain embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0023] A more complete understanding of the invention can be obtained byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

[0024]FIG. 1 is perspective view of a simplified representation of apresently preferred embodiment of a forced gas convection coolingsystem.

[0025]FIG. 2 is a perspective view of another presently preferredembodiment of a forced gas convection cooling system 100 in combinationwith a conventional wet jacketed vacuum calibration cooling system 400.

[0026]FIG. 3 is a perspective view of an embodiment of a forced gasconvection cooling system 300 using sizing templates in combination witha forced gas convection calibration cooling system 200.

[0027]FIG. 4 is a perspective view of a calibrator according to theinvention.

[0028]FIG. 5 is a perspective view of a sizing template according to theinvention.

[0029]FIG. 6 is a front perspective view of a sizing template assembly.

[0030]FIG. 7 is a front perspective view of the sizing template assemblyshown in FIG. 6.

[0031]FIG. 8 is schematic representation of the method of inducing aninternal vacuum.

[0032]FIG. 9 is a perspective view of an extruder die having twomandrels to form an extrudate with two hollows.

[0033]FIG. 10 is a section view taken along line 571-571 of FIG. 9.

[0034]FIG. 11 is a side view of a schematic representation of apresently preferred embodiment of a forced gas convection system forinternally cooling an extrudate having a hollow.

[0035]FIG. 12 is a simplified schematic representation of a forced gasconvection cooling system assisted by a refrigeration unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] While the present invention will be described fully hereinafterwith reference to the accompanying drawings, in which a particularembodiment is shown, it is to be understood at the outset that personsskilled in the art may modify the invention herein described while stillachieving the desired result of this invention. Accordingly, thedescription that follows is to be understood as a broad informativedisclosure directed to persons skilled in the appropriate art and not aslimitations of the present invention.

[0037] A simplified perspective view of a forced gas convection coolingsystem 10 is shown in FIG. 1, depicting the internal duct work of thecooling system with an external “chamber” 11 shown in phantom lines. Theframework and insulation materials have been removed for ease ofdiscussion. Forced gas convection cooling systems are described in U.S.Pat. No. 6,389,828, which is incorporated herein in its entirety. Thecooling system 10 includes a variable speed fan 12 or other suitablemeans for circulating a gas. The fan 12 includes a motor housing 14 anda blade housing 16, which encloses fan blades 18. The cooling system 10includes a back chamber 20, referred to as a “feed” chamber, and a frontchamber 22, known as the “cooling” chamber, connected by end duct 30.The end duct 30 includes an extrudate passage 32, or other opening,through which an extrudate 25 (shown in FIG. 1 after passing through thecooling system for ease of illustration) may enter or exit the coolingsystem 10, preferably traveling in a direction shown by arrow 15. Inoperation, the fan 12 preferably circulates the gas contained in thesystem in a direction shown by arrows 13, although circulation may be inthe reverse direction if desired. Gas is drawn into the blade housing16, which acts as a return chamber, from the front chamber 22 through aninlet throat 26 and discharged from the fan 12 into the back chamber 20.The gas enters the front chamber 22 from the end duct 30 through outletthroat 28, such that the gas travels through the front chamber 22 in thesame direction as the extrudate. This process can be repeated as the gasis continuously circulated through the cooling system 10 to cool anextrudate. A liquid cryogen feed line 36 is in communication with aliquid cryogen source (not shown) and is adapted to deliver liquidcryogen, such as nitrogen, to the system 10. Preferably, the feed line36 extends into the back chamber 20 and includes a spray bar 38 having aplurality of orifices to evenly inject and distribute liquid cryogen.Preferably, the feed line 36 is placed in communication with the backchamber 20 downstream from the fan 12 to inject or distribute liquidcryogen into the stream of circulated gas, which aids in thevaporization and distribution thereof before it reaches the frontchamber 22 containing the extrudate. At the presently preferredoperating temperatures of the cooling system 10, substantially completeand instantaneous vaporization of the liquid cryogen occurs upon releaseor injection into the back chamber 20 or any other suitable point ofentry. However, there may be alternative applications wherein a muchlower operating temperature may be utilized, such that there is agreater probability of the liquid cryogen not totally vaporizing. Insuch applications, a larger feed chamber (not shown) in combination withthe fan 12 can provide a region wherein substantially completevaporization of the liquid cryogen is provided, thereby reducing thelikelihood of any liquid cryogen being distributed onto the surface ofthe extrudate. The liquid cryogen is preferably liquid nitrogen,however, other cryogens such as liquid carbon dioxide, liquid air andother refrigerants having normal boiling points substantially belowminus 50° F. (−46° C.) can also be used. The liquid nitrogen expands 700times its volume in liquid state, capturing a high BTU as it transitionsto gaseous form, creating a highly effective refrigerant and rapidlyreducing the temperature in the cooling system 10. The fan 12 can becontrolled by a controller 50 to circulate the vaporized cryogen at avariable velocity through the back chamber 20, end duct 30, and frontchamber 22 where it cools the extrudate. The cooling process continues,including the injection of additional liquid cryogen into the backchamber 20 as needed to obtain, or maintain, a desired temperature inthe front chamber 22. The extrudate enters the cooling system throughthe extrudate passage 32 and travels through the front chamber 22 whereit is cooled by the circulating cryogen gas. An extrudate outlet passage40, or other opening, is provided at an end of the front chamber 22opposite the extrudate passage 32 that allows the extrudate to exit thesystem 10. Preferably, both the extrudate inlet passage and outletpassage 32 and 40 are equipped with a sealing means, such as an endtemplate (shown in FIG. 3), neoprene gasket or other means known in theart, that prevents or reduces the ingress of air and egress of vaporizedcryogen to and from the system. Optionally, the sealing means can beselected or designed to permit excess pressure in the system to ventoutside. In such a case, a separate vent may not be needed.

[0038] The cooling system 10 can further include a number of othercomponents for controlling, optimizing, and generally automating thecooling process. These other components can include a vent 34, aninternal temperature sensor 42, and a heating unit 44. The controller 50can include a microprocessor, for controlling the operation of thecooling system 10, either automatically or under the control of anoperator. The vent 34 can be provided, for example in the back chamber20 as shown, to release pressure build up which may be created by theexpansion of the liquid nitrogen as it is injected into the coolingsystem 10. The vent can simply be a small orifice and is preferablyplaced upstream of the cryogen feed line 36 and spray bar 38 anddownstream of the front chamber 22 (with respect to gas flow as shown byarrows 13) to minimize the loss of cooling capacity. By venting afterthe gas has been circulated over the hot extrudate and before the spraybar 38 distributes fresh liquid cryogen, the vented gas has removedenergy from the product and is the warmest portion of gas in the systemand therefore does not waste newly delivered liquid cryogen. Thetemperature sensor 42 can be provided in communication with the gasstream generally at any point, but is preferably in the front chamber20, back chamber 22, or end duct 30, as shown, to monitor temperature ofthe vaporized cryogen at a desired point. Alternatively, the temperaturesensor could be positioned elsewhere, such as the blade housing 16 inorder to detect the temperature of the gas stream coming into the fan12. Similarly, additional temperature sensors could be positioned atdifferent locations to detect the temperature of the gas at severalpoints in the cooling system 10. Output from the temperature sensor 42,and other sensors, if more are used, can be provided to the controller50 for use in regulating the speed of the fan 12 and controlling a valve46 provided in the cryogen feed line 36 to inject liquid cryogen intothe back chamber 20. The temperature sensor 42 can be, for example, athermocouple. The controller 50 can be programmed with the wind chillequation and can also receive a signal from the fan 12 indicative of thefan's speed. This data can be used to determine the effectivetemperature in the front chamber 22. The heating unit 44, can be asimple heating element and can be located, for example, in the backchamber 20, as shown in the figure. The heating element can be operatedby the controller to increase the temperature in the cooling system 10,if necessary, to adjust and maintain the desired ambient temperature.Multiple such cooling systems may be placed in series and operatedindependently or together.

[0039] In a preferred embodiment of the present invention, an externaltemperature sensor 48, such as an infrared temperature sensor, isprovided at a desired point downstream from the extrudate outlet passage40 to sense the temperature of the extrudate 25 after exiting the frontchamber 22. For example, the external temperature sensor 48 could beplaced adjacent the extrudate outlet passage 40 or may be placed furtherdownstream, such as adjacent a cutting assembly or puller. The externaltemperature sensor 48 senses the surface temperature of the extrudate 25and relays the output to the controller 50. The controller 50 utilizesthe output from external temperature sensor 48 in addition totemperature sensor 42 (and additional temperatures if provided) inregulating the speed of the fan 12 and controlling the valve 46 providedin the cryogen feed line 36 to inject liquid cryogen into the backchamber 20.

[0040] The controller 50 can control the speed of the fan 12, the valve46 to inject the cryogen 37 into the back chamber 20 and the heatingunit 44, and thereby closely regulate the wind chill temperature in thefront chamber 22 to correspond to, and be maintained at a desired windchill temperature to ensure that the extrudate exiting the front chamber22 has reached an optimum product temperature. The optimum producttemperature desired for the extrudate exiting the extrudate outletpassage 40 (or other point depending on where the external temperaturesensor 48 is placed) can be input to the controller 50 by an operator.The controller 50 can monitor the speed of the fan 12 (and thus thevelocity of the gas stream circulating through the front chamber 22) andfeedback from the external temperature sensor 48 and temperature sensor42 to cause the sensed temperature, or calculated wind chilltemperature, to increase or decrease depending on the externaltemperature sensor 48 reading. Thus, the controller can efficientlycontrol the cooling of the extrudate 25 to provide an optimum producttemperature (rigidity) for further processing, such as cutting theextrudate 25.

[0041] The cooling efficiency of the system can generally be optimizedby using principles of forced air convection. Extraction of heat from anextrudate 25 can be increased by blowing cooler air over a warm surface.The “effective” temperature inside the front chamber 22, or “cooling”chamber can be calculated from the ambient temperature and the velocitythat the gas (cryogen 37) is blown over the surface of the article 16using the following equation for calculating “wind chill” temperature:

T _(wc)=0.0817(3.71V ^(0.5)+5.81−0.25V)(T−91.4)+91.4

[0042] More specifically, the efficiency of the cooling system 10 can beoptimized, i.e., maximum cooling using a minimum amount of liquidcryogen 37, by controlling the speed of the fan 12. In particular, for agiven amount of liquid cryogen 37 injected into the back chamber 20 or“feed” chamber, the speed of the fan 12 can be increased in order toincrease the rate in cooling of the front chamber 22 without adding moreliquid cryogen 37. Only when the speed of the fan 12 is at its maximum,would it be necessary to inject additional liquid cryogen 37 into theback chamber 20 to further reduce the temperature in the front chamber22. Moreover, the temperature in the front chamber 22 can also beregulated to a set point temperature by adjusting the speed of the fan12, faster or slower, instead of injecting more liquid cryogen 37.Output from the external temperature sensor allows the controller 50 tomanipulate the “wind chill” within the front chamber 22 to increase ordecrease the cooling of the extrudate 25. In this sense, the coolingsystem 10 can be optimized based on the optimum product temperature.Thus, minimum necessary cooling using a minimum amount of liquid cryogen37 is achieved. In contrast, prior art cryogenic cooling systemstypically control the temperature solely by controlling the amount ofliquid cryogen injected into the system or only monitor the “windchill.” The efficiency of the system can be further optimized if itbecomes necessary to increase the temperature in the cooling chamber byusing the heating unit 44. Prior to expending energy to operate theheating unit, the speed of the fan 12 can be reduced to lower the windchill temperature, and thus decrease the rate of cooling. If reducingthe speed of the fan 12 alone is insufficient, then the heating unit 44can be operated. By reducing the speed of the fan 12 first, energy canbe conserved, thus increasing the efficiency of the cooling system 10.It should therefore be appreciated that “rate of cooling,” is dependentboth on the sensed temperature and the wind chill, i.e., “effective,”temperature. To summarize, increasing the speed of the fan 12 results inlowering the effective temperature in the front chamber 22, whichresults in an increase in the rate of cooling of the extrudate 25.Conversely, reducing the speed of the fan 12 results in an increase inthe effective temperature in the front chamber 22, which results in adecrease in the rate of cooling of the extrudate 25. Accordingly, it canbe appreciated that controlling the speed of the fan 12 and cryogeninjection in relation to the extrudate temperature after exiting the“cooling” chamber 22 can be advantageously utilized to control the“effective” temperature in the “cooling” chamber 22, and thus the rateof cooling of the extrudate 25. This prevents ineffective or unnecessary“overcooling” of the extrudate, when only the optimum producttemperature must be reached.

[0043] It also should be understood that the configuration and number ofpassageways provided to circulate the gas through the cryogenic coolingsystem, and around the article to be cooled, can be varied to suitdifferent applications and conditions. Consequently, the embodimentsillustrated are by way of example only, and are in no way intended to bean exhaustive representation of every possible configuration.

[0044] Instead of or in addition to cooling the outer surface of anarticle, vaporized cryogen can also be used to cool tooling, or articlesheld therein, by circulating cooling water or vaporized cryogen (asdisclosed in U.S. Pat. No. 6,389,828) through internal coolingpassageways, e.g., cooling circuits, provided in the tooling. Oneexample applicable to cooling extrusions is tools called calibrators. Aprior art type calibrator based cooling system 400, often referred to asa wet, vacuum-jacketed calibration tooling is shown in FIG. 2 incombination with a downstream cooling system 100 configured similarly tothe cooling system 10 shown in FIG. 1 and including a sizing templateassembly 180 positioned in front chamber 122, discussed in more detailbelow. Cooling system 100 is shown with an external chamber 111 having atop cover 124 in an open position that surrounds the front chamber 122,back chamber (not shown), end duct (not shown), etc. that is depicted inFIG. 1 with respect to cooling system 10. A fan 118 is shown positionednear a front end 120 of cooling system 100, however, the cooling systemfan is preferably positioned near the rear end (not shown) as detailedin cooling system 10 illustrated in FIG. 1. The cooling system 400includes a calibrator 112, and such a system can typically utilizeseveral, such as calibrators 112 a-g, positioned at spaced apartlocations through which an extrudate 125 is fed and thereby cooled.Water and vacuum conduits (not shown) are connected to a water manifold114 and vacuum manifold 116 respectively, such that cooling water (orvaporized cryogen) may be circulated through the internal coolingcircuits and a vacuum may be applied to the outer surface of theextrudate 125 to assist in maintaining its shape. The extrudate enterssystem 400 through a calibrator inlet passage 122, seen in calibrator112 g. A vacuum is drawn through grooves in the calibrator 112 tomaintain contact between the extrudate 125 and an inner face of thecalibrator extrudate passage. However, these prior art calibrator-basedcooling systems require costly external vacuum pumps to create an assistvacuum and often also come with the disadvantages of using coolingwater. The present invention eliminates the need for the external vacuumpumps and the associated vacuum/water conduits associated with the priorart systems.

[0045] Referring to FIG. 3, a forced gas convection calibration toolingcooling system 200 is shown in combination with a downstream forced gasconvection sizing template cooling system 300. Cooling system 200includes a fan 212 and external chamber 211 and top cover 224 thatsurrounds the remaining elements discussed in reference to coolingsystem 10 and shown in FIG. 1, including a front chamber 222. Similarly,cooling system 300 includes a fan (not shown) and external chamber 311and top cover 324 that surrounds the remaining elements discussed inreference to cooling system 10 and shown in FIG. 1, including a frontchamber 322. An end template 214 is provided on external chamber 211that includes an extrudate inlet passage 232 and provides a means ofsealing against the extrudate (not shown) as previously discussed.Optionally, fan 212 may be used to circulate vaporized cryogen throughboth cooling system 200 and 300, however, it is preferred that eachcooling system 200 and 300 have an independent fan such that the systemsmay be controlled separately or separated altogether for differentoperations. A calibrator assembly 216 is positioned within front chamber222. The calibrator assembly 216 includes individual calibrators 218 a-ecoupled to guide rail 230. The number of calibrators used in acalibrator assembly can vary from one to any number, and depending onthe requirements of the product. Likewise, the size and shape of thecalibrator(s) may vary depending on the specific product to be produced.The vaporized cryogen is circulated thorough front chamber 222 over theextrudate outer surface and the calibrators 218 a-e.

[0046] A calibrator 218 for use with cooling system is illustrated inFIG. 4. The calibrator 218 includes a product passage 220 defining aninner surface 226 that makes contact with, but also provides for thepassage of an extrudate. By making contact with the extrudate, thecalibrator 218 acts as a heat sink and removes energy from the extrudatethrough conduction. The calibrator 218 also assists the extrudate inmaintaining its extruded shape. The calibrator has an outer surface 232including a plurality of fins 234 extending outwardly therefrom andrunning substantially parallel to the center axis of the product passage220. The plurality of fins 234 define a plurality of channels 236 therebetween. Inclusion of the plurality of fins 234 greatly increases theouter surface area of the calibrator 218. By increasing the outersurface area of the calibrator 218, greater amounts of energy can bedissipated to the vaporized cryogen circulated in the cooling system200. The vaporized cryogen flows over the outer surface of thecalibrator removes energy therefrom by forced gas convection. Thegreater the outer surface area of the calibrator means greater contactwith the circulated cryogen and more heat transfer. The plurality offins 234 also increase the mass of the calibrator 218 which increasesthe amount of energy (heat) the calibrator can remove from theextrudate. Preferably, vacuum grooves 228 are provided in the innersurface 226, preferably spaced apart and extending the entirecircumference of the product passage 220. At least one pinhole (notshown) is provided from within each vacuum groove 228 and extending tothe outer surface, such that the pressure realized outside of thecalibrator 218 is also communicated to the vacuum groove 228.Preferably, a pinhole is provided at the bottom of each channel 236 suchthat a single vacuum groove includes a plurality of pinholes incommunication with the atmosphere outside the calibrator 218. Therefore,production of a vacuum within the front chamber 222 is transferred tothe vacuum grooves 228. A vacuum within the vacuum grooves 228 assistsin maintaining the extrudate in contact with the calibrator, which inturns ensures a proper shape and advantageous conductive heat transfer.Preferably, the calibrator includes at least one guide slot 238 adaptedto provide passage of a guide rail 230 (see FIG. 3) such that thecalibrator 218 may be secured in a cooling system. A setscrew 240 allowsthe calibrator 218 to be tightly secured to the guide rail 230.

[0047]FIG. 5 illustrates a sizing template 318, another type of toolingthat may be used with the present invention, that is similar to thecalibrator 218 shown in FIG. 4. The sizing template 318 includes aproduct passage 320 defining an inner surface 326 that makes contactwith, but also provides for the passage of an extrudate. The sizingtemplate 318 has an outer surface 332 including a plurality of fins 334extending outwardly therefrom and running substantially parallel to thecenter axis of the product passage 320. The plurality of fins 334 definea plurality of channels 336 there between. As previously discussed,inclusion of the plurality of fins 334 greatly increases the outersurface area of the sizing template 318. Optionally, a circumferentialrib 328 is provided in the inner surface 326. Several such ribs may beincorporated, preferably spaced apart and extending the entirecircumference of the product passage 320. Preferably, the sizingtemplate 318 includes at least one guide slot 338 adapted to providepassage of a guide rail 130 (see FIG. 2) such that the sizing template318 may be secured in a cooling system (see FIG. 2). A setscrew 340allows the sizing template 318 to be tightly secured to the guide rail130.

[0048]FIGS. 6 and 7 depict a front perspective and rear perspective,respectively, of a sizing template assembly 182 including an extrudate225 passing through the product passages in the direction of arrow 186.Although, the foregoing description is made with respect to a sizingtemplate assembly, a calibrator assembly for use with the presentinvention may be structure in the same general way. The assembly 182includes a plurality of sizing templates 318 positioned on four guiderails 184. Preferably each sizing template 318 is positioned adjacent toa complimentary deflector plate 340. As best seen in FIG. 6, eachdeflector plate 340 includes gas flow passages 342 that are adapted toguide the flow of vaporized cryogen over/through the plurality of fins334 extending from the outer surface of the sizing template 318. Thedeflector plate preferably includes a spoiler 344 (FIG. 7) extendingfrom a backside 346 of the deflector plate in a generally downwarddirection. The spoilers 344 operate to direct the gas flow along theouter surface of the extrudate 225. The assembly 182 is adapted to beplaced within the front or “cooling” chamber of a forced gas convectioncooling system.

[0049] The forced gas convection calibration cooling system 200 andother forced gas convection cooling systems according to the inventiondo not require separate external vacuum pumps to provide vacuumassistance to the calibrators and other tools. Advantageously, thecooling system 200 may be operated to internally induce a vacuum withinthe front chamber 222 or “cooling”/calibration chamber. Referring backto FIG. 1 and cooling system 10, which illustrates the internalduct-work and system components included in the forced gas convectioncooling systems according to the present invention, gas flow enters thefront chamber 22 from the end duct 30 via outlet throat 28 and exits thefront chamber 22 to the blade housing 16 of fan 12 via inlet throat 26.A vacuum is generated in the front chamber by operating the fan 12 andrestricting the flow of gas into the front chamber 22. Preferably, thisis accomplished by ensuring that the cross-sectional area of the outletthroat 28 is less than the cross-sectional area of the inlet throat 26.In this manner, the fan 12 is “starved” and produces a vacuum in thefront chamber. The vacuum produced in the front chamber can easily reach15 inches of water, but varies depending on the strength of the fan 12.Such an internally induced vacuum can be produced with any forced gasconvection system having a substantially “captive” system meaning thatthe gas circulation is a closed loop. Preferably, the outlet throat 28is of a similar cross-sectional area as the inlet throat 26 but isaffixed with a restrictor plate (not shown) which can be mechanicallyoperated (manually or by a solenoid actuator driven by the controller50) to vary the cross-sectional area of the outlet throat 28. Thus, thecontroller 50 can manipulate and control the pressure within the frontchamber 22. A pressure sensor may be provided to sense the pressurewithin the front chamber 22 and send feedback to the controller 50 whichthen adjusts the cross-sectional area of the outlet throat 28 and hencethe pressure. In a reverse scenario, if a positive pressure is requiredwithin the front chamber 22, then the cross-sectional area of the outletthroat 28 should be larger than the cross-sectional area of the inletthroat 26. In this instance, the inlet throat 26 can also be providedwith a similar restrictor plate and control or simply designing theoutlet throat 28 and restrictor plate such that a cross-sectional areaof the outlet throat 28 can vary from an area less than to an areagreater than the cross-sectional area of the inlet passage 26. Referringto FIGS. 1-3, operation of the cooling systems 10, 100, 200 and 300accordingly can provide a reduced pressure or “vacuum” within frontchambers 22, 122, 222 and 322 respectively. FIG. 8 depicts a schematicrepresentation of the method of creating an internally induced vacuumwithin the “cooling” chamber of a forced gas convection cooling system.Operation of the fan 3 and maintaining a cross-sectional area of inlet 2into front chamber 5 less than the cross-sectional area of outlet 4produces a vacuum in the front chamber 5.

[0050] Another preferred embodiment of the present invention isillustrated by FIGS. 9-11. FIG. 11 shows a simplified version of aforced gas convection cooling system 500 for internally cooling anextrusion having a hollow profile. The components and operation of thecooling system 500 are generally the same as for the cooling systems 10,200 and 300 illustrated in FIGS. 1-3, except that an outlet conduit 520and the extrudate 525 essentially replace the front and back chambers.In particular, a source 509 of liquid cryogen 537, preferably liquidnitrogen, the injection of which into the cooling system through spraybar 538 can be controlled by a feed valve 546 placed in feed line 536,which itself can be operated by a controller 550. As previouslydiscussed, the liquid cryogen 537 substantially instantaneouslyvaporizes and cools the gas stream circulated by the fan 512, preferablyin a direction shown by arrows 513. The vaporized cryogen stream iscommunicated to an extruder die 570 via outlet conduit 520. Extruder die570 is shown in more detail in FIGS. 9 and 10. Extruder die 570 includesan inlet bore 572 extending from an outer surface 574 of the extruderdie 570 through a mandrel 576 that is adapted to form an extrudatehollow 578 within the extrudate 525. The inlet bore 572 is adapted to beplaced in fluid communication with the outlet conduit 520 and therebypass vaporized cryogen through the extruder die 570 and mandrel 576 andinto the extrudate hollow 578. Preferably, the inlet bore 572 and outletconduit are separably coupled such that different dies can beinterchanged for different product configurations. Inlet bore 572terminates at a mandrel outlet 586 where vaporized cryogen may enter theextrudate hollow 578. Optionally, an outlet extension 580 is provided toensure that the pressure exerted by the vaporized cryogen as it isintroduced into the extrudate hollow 578 is spaced from a leading edge582 of the die 570. Optionally, the cooling system 500 is used incombination with an external forced gas convection cooling system, suchas described in systems 10, 100, 200 and 300 (shown in phantom in FIGS.10 and 11), that are placed substantially adjacent the die 570, but asmall separation 584 may exist. If the outlet extension 580 is not used,then a positive pressure within the extrudate hollow 578 may cause abubble or distortion within the small separation that is undesirable.Preferably, a forced gas convection calibration cooling system, such ascooling system 200, is used immediately adjacent the extruder and incombination with cooling system 500. In this scenario, the outletextension is selected to have a length such that the vaporized cryogenis released at a point within the length of a calibrator and thedistortion problem is thus minimized. Preferably, mandrel outlet 586 andoutlet extension 580 are separably coupled, such as with threads 588, sothat different length extensions may be used. The outlet extension 580includes a nozzle 590 or other means for directing the flow of vaporizedcryogen onto an inner surface of the extrudate 525, as shown by arrows592.

[0051]FIG. 9 depicts a die 570 a configuration including two mandrels576 a and 576 b that form extrudate hollows 578 a and 578 b, but do notinclude outlet extensions. An outlet conduit manifold (not shown) can beprovided to provide more than one vaporized cryogen streams to twoseparate outlet conduits 520 a and 520 b and inlet bores, or an inletbore manifold (not shown) may be provided to split a single vaporizedcryogen stream into any number of inlet bores to provide vaporizedcryogen to extrudate hollows. Splitting a single stream ensures that thetemperature of the vaporized cryogen streams entering different hollowsis substantially the same. However, depending on the profile of anextrudate, it may be desirable to provide each hollow with streams of adifferent temperature. In this case, each hollow that requires aseparate temperature is placed in communication with a separate forcedgas convection cooling system as herein disclosed.

[0052] Referring again to FIG. 11, temperature sensors 542 a and 542 bcan be provided for detecting the ambient temperature in the outletconduit 520, preferably at a point downstream from liquid cryogen spraybar 538, or within cutting chamber 560 and outputting that informationto the controller 550. Additionally, an external temperature sensor 548,such as an infrared sensor, can be provided that outputs a producttemperature reading to the controller 550 as discussed with respect tocooling system 10 illustrated in FIG. 1. An outlet conduit valve 562 cansimilarly be operated by the controller 550. A heating unit 564 can beprovided that is operable by the controller to input heat to the systemif necessary. A conveyor system 558 can similarly be used to support theextrudate 525 between the extruder and any downstream equipment. Thecontroller 550 can regulate the temperature in the outlet conduit bycontrolling the fan 512 and the feed valve 546 based upon feedback fromthe temperature sensor 542 a, the temperature sensor 542 b, the externaltemperature sensor 548 or all three sensors. The controller 550 isprogrammed to operate system 500 in a similar manner as disclosed forsystem 10 to optimize the system's efficiency using principles of forcedgas convection. The controller can regulate the speed of the fan 512,operate feed valve 546 to control release of liquid cryogen 537 intooutlet conduit 520 and the heating unit 564 to closely regulate the“wind chill” temperature within the extrudate hollow 578 to correspondto, and be maintained at the desired wind chill temperature which can beinput by an operator. Optionally, the controller 550 can also act as thecontroller for additional cooling systems, such as systems 10, 100, 200and 300 discussed herein, used in combination with cooling system 500.

[0053] Preferably, the cooling system 500 is captive, i.e., closed, suchthat substantially no outside air enters the vaporized cryogen and thevaporized cryogen is recirculated. The extrudate 525 enters the closedcutting chamber 560 through an inlet portion (not shown) and exitsthrough a similar outlet portion (not shown) provided with appropriatesealing portions as known to those in the art. Cutting chamber 560includes a means for severing the extrudate 525 into desired lengths forfurther processing or as the final product. The extrudate 525 enters thecutting chamber 560 through a cutting chamber inlet (not shown) providedwith appropriate sealing portions as known to those in the art. A saw(not shown) or other suitable cutting means is housed in the cuttingchamber 560 and is operated to periodically cut the extrudate 525 intopredetermined lengths. Care should be taken such that during the cuttingstroke, the vaporized cryogen is allowed to escape from within theextrudate hollow 578, such as through a saw blade (not shown) providedwith slots. The slots prevent a positive cryogen pressure build-upwithin the extrudate 525 during the cutting stroke. If a continuousblade is used, even the brief amount of time required for the cuttingstroke may cause a blockage of the flow of cryogen through the extrudatehollow 578, and thus cause bellowing and distortion of the product aswell as increased drag on tooling equipment. Return conduit 566 channelsthe vaporized cryogen back to the variable speed fan 512. A vent 568 andvent valve 569 are provided to allow pressure in the system to becontrolled by the controller 550. Pressure sensor 567 can give feedbackto the controller 550 which then operates the vent valve 569, fan 512,feed valve 546, and outlet conduit valve 562 to vary the pressure withinthe system. Additional pressure sensors may be included at other pointswithin the system to give feedback to the controller 550. Optionally, aheat exchanger 568, e.g., a shell and tube exchanger, is provided topre-cool the recirculated cryogen and thus reduce the consumption ofliquid cryogen 537. A heating element 50 may be provided incommunication with the circulated cryogen 24, such as in the returnconduit 42 as shown, such that heat may be added to the system ifnecessary.

[0054] Advantageously, the present invention allows an extrudate with ahollow profile to be cooled from the outside and from within. Theinternal and external surfaces of the extrusion can be cooled at equalor variable rates, which allows for extensive process control heretoforeunseen. The present invention, by providing cooling from within theextrusion, provides for quicker cooling and shorter cooling chamberlengths. Also, the internal gas flow of cryogen provides a positivepressure against the internal surfaces of the extrusion, which in turnreduces or eliminates the need for an external vacuum on the outersurface of the extrudate to provide a quality product. Since lessexternal vacuum is required, the amount of drag between the product andtooling is reduced, which provides for increased rates of production andsmaller downstream, equipment such as pullers.

[0055] A simplified perspective view of a forced gas convection coolingsystem 610 assisted by refrigeration is shown in FIG. 12, depicting theinternal duct work of the cooling system with an external chamber 611shown in phantom lines. The framework and insulation materials have beenremoved for ease of discussion and illustration. The cooling system 610may include similar components as described for cooling system 10depicted in FIG. 1, including a variable speed fan 612 or other suitablemeans for circulating a gas. The cooling system 610 further includes aback chamber 620 and a front chamber 622 connected by end duct 630. Theend duct 630 includes an extrudate passage 632, or other passage,through which an extrudate 625 may enter or exit the cooling system 610,preferably traveling in a direction shown by arrows 615. A secondextrudate passage 640 is positioned at an opposing end of the frontchamber 622, such that the extrudate 625 may enter or exit the coolingsystem 610. Preferably, each of the first and second extrudate passages632 and 640 include appropriate seals 634, 635 that prevent leakage ofgas to and/or from the system. Optionally, the seals 634, 635 may bedesigned to permit excess pressure in the system to vent to the outside.Preferably, the cooling system 610 is captive, i.e., closed, such thatsubstantially no outside air enters the vaporized cryogen and thevaporized cryogen is recirculated. Preventing the ingress of air allowsa “dry” atmosphere to be maintained within the system, the advantages ofwhich are made more apparent below.

[0056] In operation, the cooling system 610 operates in a similarfashion to that discussed previously in relation to cooling system 10.The fan 625 circulates the gas contained within the system, preferablyin a direction shown by arrows 613. Gas is drawn into blade housing 616from the front chamber 622 through inlet throat 626 and discharged fromthe fan 612 into the back chamber 620. The fan 612 and blade housing 616are depicted in FIG. 12 at a position central to the length of the backchamber 620 for ease of illustration. Preferably, the fan 612 ispositioned just downstream from the inlet throat 626, although the fanmay placed at any desired position within the system that allows for thecirculation of the gas contained therein. The gas enters the frontchamber 622 through end duct 630 and outlet throat 628. The systemincludes a liquid cryogen feed line 636 in communication with a sourceof liquid cryogen (not shown) and is adapted to deliver liquid cryogento the system. Preferably, the feed line 636 extends into the backchamber 620 and includes a spray bar 638 preferably having a pluralityof orifices to evenly inject and distribute liquid cryogen. Preferably,the feed line 636 is placed in communication with the back chamber 620downstream from the fan 612 to inject or distribute liquid cryogen intothe stream of circulated gas, which aids in the vaporization anddistribution thereof before it reaches the front chamber 622 containingthe extrudate. At the presently preferred operating temperatures of thecooling system 610, substantially complete and instantaneousvaporization of the liquid cryogen occurs upon release or injection intothe back chamber 620 or any other suitable point of entry. The liquidcryogen is preferably liquid nitrogen, however, other cryogens such asliquid carbon dioxide and other refrigerants having normal boilingpoints substantially below minus 50° F. (−46° C.) can also be used. Theliquid nitrogen expands 700 times its volume in liquid state, capturinga high BTU as it transitions to gaseous form, creating a highlyeffective refrigerant and rapidly reducing the temperature in thecooling system 610. The fan 612 can be controlled by a controller 650 tocirculate the vaporized cryogen at a variable velocity through the backchamber 620, end duct 630, and front chamber 622 where it cools theextrudate.

[0057] The cooling system 610 advantageously includes a refrigerationunit 623. The refrigeration unit may be selected from mechanical(vapor-compression) refrigeration, vapor-absorption refrigeration or anyother refrigeration means known in the art. Preferably, therefrigeration unit 623 comprises a conventional vapor-compression systemand includes conventional components such as a compressor (not shown), acondenser (not shown), a liquid storage vessel (not shown), a throttlingvalve (not shown), a refrigerant (not shown) and an evaporator 627. Theoperation of such a system is well known to those skilled in the art.Generally, the refrigerant is a liquid which partly vaporizes and coolsas it passes through the throttling valve. Common refrigerants includeammonia, sulfur dioxide, and various halides of methane and ethane. CFCshave been used extensively in the past, but due to their adverseenvironmental effects, are generally avoided now. In operation, thecompressor inputs work to maintain nearly constant pressures on eitherside of the throttling valve. The mixed liquid and vapor entering theevaporator 627 from the throttling valve is colder than the atmospheresurrounding the evaporator 627, thus the liquid/vapor refrigerantabsorbs heat from the interior of the refrigerator box (back chamber620) and completely vaporizes. The vapor is then forced into thecompressor, where its temperature and pressure increase as the result ofcompression. The compressed vapor then travels into the condenser, whereit cools down and liquefies as the heat is transferred to the colderatmosphere surrounding the condenser's cooling coils. The liquefiedrefrigerant is then stored in the storage tank for re-release throughthe throttling valve into the evaporator. As shown in FIG. 12, theevaporator 627 or “cooling coil” of the mechanical refrigeration unit ispositioned within the back chamber 620, such that the evaporator 627 isin energy absorbing communication with the vaporized cryogen beingcirculated therethrough. The evaporator 627 comprises a cooling conduit629, which allows the refrigerant to circulate through the unit 623 asbriefly described above. The cooling conduit 629 is shown with aplurality of fins 629 a that increase the surface area of the coolingconduit 629, which in turn provides for quicker energy absorption fromthe surrounding atmosphere.

[0058] Preferably, the atmosphere contained within the system 610 ispurged with vaporized cryogen prior to operating the mechanicalrefrigeration unit 623. By initially venting the system and due to thehigh expansion ratio of the liquid cryogen, an initial release ofcryogen substantially replaces the pre-operation atmosphere with asubstantially “dry” vaporized cryogen atmosphere. This advantageouslyremoves substantially all moisture-containing air that may have been inthe system, such that only the “dry” vaporized cryogen is circulated.The cooling system 610 is preferably a closed system such that moist airdoes not enter. The closed system may be maintained by operating at aslight positive pressure within the system after the initial purge. Inthis regard, gas escapes, but no air is allowed into the system thatwould provide moisture to freeze on and clog the evaporator 627. Withoutmoisture in the system, the evaporator 627 does not become clogged withice and can cost-effectively provide cooling to very low temperatures.Thus, the need to introduce new liquid cryogen into the back chamber 620to lower the temperature of the circulated vapor is reduced. Reducingthe consumption of liquid cryogen advantageously increases the costefficiency of a forced gas convection cooling system.

[0059] The cooling process preferably continues by circulating the gaswithin the system to cool the extrudate 625. As the circulating gasdraws heat from the extrudate, the temperature of the gas rises.Operation of the refrigeration unit 623 acts to remove heat from thecirculating gas and thereby assists in maintaining a desiredtemperature. The cooling system 610 still provides the option ofinjecting additional liquid cryogen into the back chamber 620 as neededto obtain, or maintain, a desired temperature in the front chamber 622.Such injections are reduced by the inclusion and operation of therefrigeration unit 623. The extrudate enters the cooling system throughthe first extrudate passage 632 and travels through the front chamber622 where it is cooled by the circulating cryogen gas and then exitsthrough the second extrudate passage 640. Preferably, both the first andsecond extrudate passages 632 and 640 are equipped with the seals 634,635 or other sealing means, such as an end template (shown in FIG. 3),neoprene gasket or other means known in the art, that prevents orreduces the ingress of air and egress of vaporized cryogen to and fromthe system.

[0060] The cooling system 610 can further include a number of othercomponents for controlling, optimizing, and generally automating thecooling process as previously discussed with the other embodiments.These other components can include a vent 634, an internal temperaturesensor 642, a heating unit 644 and external temperature sensor (notshown). The inlet and outlet throats 626 and 628 may also be designed toprovide for an internally induced vacuum as previously described. Thecontroller 650 can include a microprocessor, for controlling theoperation of the cooling system 610, either automatically or under thecontrol of an operator. Output from the temperature sensor 642, andother sensors, if more are used, can be provided to the controller 650for use in regulating the amount of cooling provided by the mechanicalrefrigeration unit 623, the speed of the fan 612, and controlling avalve 646 provided in the cryogen feed line 636 to inject liquid cryogeninto the back chamber 620. The controller 650 can be programmed with thewind chill equation and can also receive a signal from the fan 612indicative of the fan's speed. This data can be used to determine theeffective temperature in the front chamber 622. The controller 650 canthen manipulate the cooling rate of the mechanical refrigeration unit623 directly by operation of the compressor and throttling valve, or bycommunicating to a separate refrigeration control unit (not shown),which in turn controls the flow of refrigerant through the refrigerationunit 623. The controller 650 may also manipulate the speed of the fan612 and dispensing of additional liquid cryogen to efficiently maintainthe desired wind chill for an appropriate cooling rate of the extrudate625. The operation of the refrigeration unit 623 advantageously providesheat removal from the circulating gas and thereby reduces theconsumption of liquid cryogen.

[0061] The mechanical refrigeration unit 623 may be advantageouslyincorporated into any forced gas convection cooling system, such asthose discussed herein and those disclosed in U.S. Pat. No. 6,389,828,to reduce the consumption of liquid cryogen. Multiple such coolingsystems may be placed in series and operated independently or together.Further, the mechanical refrigeration unit may be advantageouslyincluded in the other cooling system embodiments discussed hereinincluding in combination with cooling systems for internally cooling anextrusion having a hollow and in combination with forced gas convectioncooling systems incorporating a metal tooling, such as the wet-jacketedcalibration tooling system, a forced gas convection calibration toolingsystem and/or a sizing template. Use of the refrigeration unit 623 incombination with the principles of forced gas convection of a vaporizedcryogen advantageously provides for cooling systems requiring less spacethan conventional cooling water systems, capable of reaching andmaintaining temperatures below refrigeration alone, and consume lessliquid cryogen.

[0062] Various features of the invention have been particularly shownand described in connection with the illustrated embodiments of theinvention, however, it must be understood that these particularembodiments merely illustrate and that the invention is to be given itsfullest interpretation within the terms of the appended claims.

What is claimed is:
 1. A method of cooling an article comprising: a)introducing liquid cryogen into a feed chamber wherein said liquidcryogen is substantially vaporized; b) circulating said vaporizedcryogen from said feed chamber into a separate cooling chambercontaining said article to be cooled; c) circulating said vaporizedcryogen from said feed chamber into said cooling chamber and around saidarticle in said cooling chamber to cool said article; and d) operating arefrigeration unit having an evaporator in heat transferring contactwith said vaporized cryogen to remove heat from said vaporized cryogen.2. The method of claim 1 further comprising: e) sensing the temperaturein at least one of said feed chamber and said cooling chamber; f)calculating a wind chill temperature in said cooling chamber, said windchill temperature being a function of the temperature in said coolingchamber and the velocity at which said vaporized cryogen is circulatedthrough said cooling chamber over said article; and g) controlling theremoval of heat by said refrigeration unit to maintain a desired windchill temperature within said cooling chamber.
 3. The method of claim 1further comprising: e) sensing the temperature in at least one of saidfeed chamber and said cooling chamber; f) calculating a wind chilltemperature in said cooling chamber, said wind chill temperature being afunction of the temperature in said cooling chamber and the velocity atwhich said vaporized cryogen is circulated through said cooling chamberover said article; and g) controlling said velocity to cause said windchill temperature to correspond to a desired wind chill temperature. 4.The method of claim 1 further comprising controlling introduction ofadditional liquid cryogen into said feed chamber to cause thetemperature therein to correspond to a desired temperature.
 5. Themethod of claim 2 wherein cooling efficiency is optimized comprising: a)first operating said refrigeration unit to increase removal of heat fromsaid vaporized cryogen; b) thereafter increasing said velocity to amaximum velocity to increase said rate of cooling of said article; andc) thereafter introducing additional liquid cryogen only when necessaryto at least one of maintain and increase said rate of cooling such thata maximum cooling rate is achieved using a minimum amount of liquidcryogen.
 6. The method of claim 3 wherein cooling efficiency isoptimized comprising: a) first operating said refrigeration unit toincrease removal of heat from said vaporized cryogen; b) thereafterincreasing said velocity to a maximum velocity to increase said rate ofcooling of said article; and c) thereafter introducing additional liquidcryogen only when necessary to at least one of maintain and increasesaid rate of cooling such that a maximum cooling rate is achieved usinga minimum amount of liquid cryogen.
 7. The method of claim 1 furthercomprising venting pressure build-up in at least one of said feedchamber and said cooling chamber due to at least said introducing saidliquid cryogen in said feed chamber.
 8. The method of claim 1 whereinsaid feed chamber and said cooling chamber are a plurality of feedchambers and cooling chambers and each of said plurality of feedchambers and cooling chambers are individually controllable to at leastone of introduce said liquid nitrogen, vaporize said liquid cryogen,operate said refrigeration unit and circulate said vaporized cryogen. 9.The method of claim 8 wherein cooling efficiency is optimizedcomprising: a) first increasing said operation of said refrigerationunit to a maximum heat removal to at least one of maintain and increasesaid rate of cooling of said article; b) thereafter increasing saidvelocity to a maximum velocity to at least one of maintain and increasesaid rate of cooling of said article; and c) thereafter introducingadditional liquid cryogen only when necessary to at least one ofmaintain and increase said rate of cooling such that a maximum coolingrate is achieved using a minimum amount of liquid cryogen.
 10. Themethod of claim 9 further comprising heating each of said at least oneof said plurality of feed and cooling chambers to increase thetemperature therein to cause the temperature to correspond to saiddesired temperature.
 11. The method of claim 10 wherein efficiency isoptimized comprising: a) first decreasing said velocity to decrease saidrate of cooling; and b) thereafter increasing the temperature in each ofat least one of said plurality of feed and cooling chambers only whennecessary to at least one of maintain and decrease said rate of coolingsuch that a desired rate of cooling is achieved using a minimum amountof energy.
 12. The method of claim 1 wherein said article is one of aplurality of individual articles and a generally continuously producedarticle, the method further comprising feeding said one of a pluralityof individual articles and a generally continuously produced articlethrough said cooling chamber for cooling thereof.
 13. An apparatus forcooling an article comprising: a) a feed chamber; b) a source of liquidcryogen; c) an inlet into said feed chamber in fluid communication withsaid source of liquid cryogen; d) a valve disposed between said inletand said source of liquid cryogen, said valve controllable to admit saidliquid cryogen into said feed chamber, said liquid cryogen at leastpartially vaporizing in said feed chamber; e) a cooling chambergenerally separated from said feed chamber; f) at least one intakepassage connecting said feed chamber and said cooling chamber, said atleast one intake passage providing fluid communication therebetween; g)means for circulating said vaporized cryogen in said feed chamber to atleast one of aid in substantial vaporization of said liquid cryogenwithin said feed chamber and circulate said vaporized cryogen in saidcooling chamber via said at least one intake passage to cool saidarticle; h) a refrigeration unit having an evaporator adapted to absorbheat from a surrounding atmosphere, said evaporator being positioned inenergy absorbing communication with said vaporized cryogen, saidrefrigeration unit controllable to remove heat from said vaporizedcryogen.
 14. The apparatus of claim 13 further comprising: h) atemperature sensor for sensing temperature in at least one of said feedchamber and said cooling chamber; i) said means for circulatingcontrollable at variable speeds to circulate said vaporized cryogen oversaid evaporator and said article at a variable velocity to create avariable wind chill temperature in said cooling chamber; and j) acontroller connected to said temperature sensor, said controllercontrolling at least one of said refrigeration unit and said means forcirculating to cause said wind chill temperature to correspond to adesired wind chill temperature.
 15. The apparatus of claim 14 furthercomprising said valve controllable by said controller to introduce saidliquid cryogen into said feed chamber to cause the temperature in atleast one of said feed chamber and said cooling chamber to correspond toa desired temperature.
 16. The apparatus of claim 13 wherein apparatusfurther comprises: a) a return chamber communicating with a return sideof said means for circulating; b) at least one return passage connectingsaid cooling chamber and said return chamber, said at least one returnpassage providing fluid communication therebetween; and c) said meansfor circulating further circulating said vaporized cryogen from saidcentral cooling chamber to said return chamber via said at least onereturn passage.
 17. The apparatus of claim 16 wherein said at least oneintake passage and at least one return passage further comprise at leasttwo intake passages and at least two return passages.
 18. The apparatusof claim 13 further comprising: a) a pair of openings provided ingenerally opposing sides of said cooling chamber through which anarticle to be cooled may be passed to be cooled in said central coolingchamber; and b) a seal at each of said pair of openings to maintain saidcooling chamber generally sealed from the atmosphere.
 19. The apparatusof claim 13 further comprising a heating unit disposed in at least oneof said feed chamber and said cooling chamber, said heating unitcontrollable by said controller to raise the temperature in at least oneof said feed chamber and said cooling chamber to cause the temperaturetherein to correspond to a desired temperature.
 20. The apparatus ofclaim 13 further comprising a vent in communication with at least one ofsaid feed chamber and said cooling chamber to release pressure thereinresultant from at least vaporization of said liquid cryogen therein whensaid pressure reaches a predetermined level.
 21. The apparatus of claim15 wherein: a) said feed chamber and said cooling chamber furthercomprise a plurality of feed and cooling chambers, each of saidplurality of feed chambers having at least said source of liquidcryogen, said inlet, said valve, said means for circulating, saidrefrigeration unit and said temperature sensor; and b) said controllerproviding a desired temperature in each of said plurality of feed andcooling chambers independently of others of said plurality of feed andcooling chambers.
 22. The apparatus of claim 21 wherein said controllerfurther comprises a plurality of controllers, each of said plurality ofcontrollers associated with a respective one of said plurality of feedand cooling chambers.
 23. The apparatus of claim 13, wherein saidcooling chamber includes at least one metal tooling device adapted tomake cooling contact with said article.
 24. The apparatus of claim 23,wherein said at least one metal tooling device is selected from acalibrator and a sizing template.
 25. An apparatus for cooling anarticle comprising: a) a feed chamber; b) a source of liquid cryogen influid communication with said feed chamber; c) a valve disposed betweensaid source of liquid cryogen and said feed chamber, said valvecontrollable to admit said liquid cryogen into said feed chamber, saidliquid cryogen at least partially vaporizing in said feed chamber; d) acooling chamber generally separated from said feed chamber and in fluidcommunication therewith, said cooling chamber adapted to contain saidarticle for cooling; g) means for circulating said vaporized cryogen insaid feed chamber to at least one of aid in substantial vaporization ofsaid liquid cryogen within said feed chamber and circulate saidvaporized cryogen to said cooling chamber to cool said article; and, h)a refrigeration unit, said refrigeration unit having an evaporatoradapted to absorb heat from a surrounding atmosphere, said evaporatorbeing positioned in energy absorbing communication with said vaporizedcryogen.